In 1968, France exploded a hydrogen bomb over a South Pacific testing ground and became the world's fifth thermonuclear power. The Canopus test used a 3 tonne device suspended at an altitude of 600 m from a balloon over Fangataufa Atoll, 41 km south east of Moruroa. The project was led by a young physicist, Roger Dautry.This was France's largest nuclear device. It produced a yield of 2.6 megatons, and used a lithium-6 deuteride secondary jacketed with highly enriched uranium. The resulting contamination of the atoll kept it off limits to humans for six years, after which France resumed their nuclear program there with underground tests. Dark Sun: The Making of the Hydrogen Bomb, by Richard Rhodes. - book suggestion.